You should resume normal fertility right away. *Your* normal. So if you had irregular periods or trouble with fertility before that could be the case now. Also, I think that it could take a month or so for the localized Mirena hormones to fade out aif you have a Mirena.
I got my copper one out 1-2 weeks before my Dec. period was due, got my period on time. Nothing in January (spent lots on pg tests!). Then on time in February. Tested + in March. I was surprised it was so fast b/c it took a long time to TTC ds. My periods were always normal with the copper IUD but never before. I don't know what routine they would have settled into if I hadn't gotten pg.